1. Field of the Invention
The invention relates to an apparatus for the manufacture of corrugated plastic pipes with cross grooves, in which half shells, which are provided with a mold recess and combine in pairs to form a mold in a molding path which runs in the direction of production, are disposed to circulate on a horizontal machine bed, which is provided with a cover plate of antifriction metal; the half shells resting by their lower bearing surfaces on the cover plate and being pressed together transversely of the direction of production by means of a guide; an extrusion head of an extruder being disposed upstream of the molding path; the half shells being provided with vacuum ducts, which are connected to the respective mold recess and which, in the molding path, open into vacuum connections formed in the machine bed; and the half shells being provided with coolant lines, which, in the molding path, open into coolant connections and coolant outlets formed in the machine bed.
2. Background Art
In an apparatus of the generic type known from U.S. Pat. No. 4,492,551, the half shells, which combine in pairs to form a mold, are displaced while sliding on a horizontal machine bed. For a sliding motion almost free from friction and wear to be attained, the machine bed has a cover plate of an antifriction metal, for instance of bronze, on which to displace the half shells of steel. Cooling water supply and discharge takes place via corresponding connections in the machine bed, the water line inlets and outlets which are formed in the half shells overlapping these connections on the molding path. The same applies to the vacuum ducts.
EP 0 359 089 B1 teaches an apparatus for the manufacture of corrugated plastic pipes, in which the half shells, which combine in pairs to form a mold, are guided on two chains which rest one on top of the other. Support elements are fixed to the chains, on which the half shells are replaceably mounted. The vacuum ducts and the cooling water lines must be guided through these support elements to the half shells. This requires extraordinarily complicated constructions. The guidance of the water lines and the vacuum ducts is complicated, which can lead to losses of cooling water and vacuum after a comparatively short operating time. Wear occurs on the parting planes between the half shells and the support elements; this can lead to a misalignment of the half shells after a short operating time and thus to increased tolerances in the corrugated pipes to be produced.
DE 197 02 647 C1 teaches an apparatus for the manufacture of corrugated plastic pipes, in which the half shells are replaceably fixed on guide and slide elements.
It is an object of the invention to embody an apparatus of the generic type so that an increase in capacity is feasible without an increase in wear at a low construction cost.
According to the invention, this object is attained by each half shell having a core, which consists of a metal of a higher thermal conductivity and a lower specific gravity than steel, in which the mold recess is formed, in which the vacuum ducts are formed at least substantially, and which is sheathed at least in the shape of an L by a base body of steel, on which the bearing surface is formed and on which rests the guide. Based on the measures according to the invention, only unimportant constructional requirements are needed to ensure that the half shells consist at least to a considerable extent of an excellently heat conducting and lightweight material. This offers the possibility of accelerating the production rate, accompanied with sufficiently good heat dissipation. No substantial wear will occur due to the fact that the guides, which press the half shells together, bear against steel and the half shells slide by their lower bearing surfaces on the cover plate of antifriction metal. The coolant and the vacuum are transferred via only one sealing and sliding surface, namely via the machine bed directly into the half shellsxe2x80x94as in the apparatus of the generic type.
The embodiment according to which the core is at least substantially provided with a rectangular cross section with outer surfaces, on which rest inner surfaces of the base body, ensures that the core rests over its full surface in the base body, which ensures good thermal conductivity. When the base body is formed in one piece and when the base body is approximately C-shaped and holds the core, this reflects a simple design, featuring an especially stable half shell which nevertheless possesses the advantages of the invention. In particular in the case of this design, the core may have varying mold recesses; the base body may be used for cores of varying mold recesses. In this embodiment, the cooling water lines may be formed in the base body so that no problems of sealing will occur. A multi-piece, in particular two-piece design consists in that the base body is comprised of a lower plate and a plate-type vertical web and in that the base body is formed in two pieces.
The direct contact between neighboring half shells takes place via the base bodies, i.e. via the metal of greater stability, namely steel, which helps avoid wear of the core. This is especially advantageous in the embodiments according to which half shells which adjoin in the direction of production in the molding path bear against each other by their base bodies and according to which the half shells which combine in pairs to form a mold bear against each other by their base bodies in the molding path.
A particularly low-wear guide comprises guide rollers mounted by means of rolling bearings. A preferred material for the core is aluminum or an aluminum alloy. In another modified embodiment the core has a semi-cylindrical outer surface.
Further features, advantages and details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.